(1) Field of the Invention
This invention generally relates to tape threading devices, especially those used in tape drive systems. More particularly this invention is concerned with automatically threading leader block mounted tapes from their supply reels, past transducer heads, and on to take-up reels. Perhaps the most common transducer heads associated with this art are the magnetic read/write heads used to transfer information to and from magnetic tapes. Magnetic tapes of this kind are usually utilized in conjunction with tape cassette mechanisms.
(2) Description of the Prior Art
Various devices have been developed for automatically threading tapes from supply reels to take-up reels. In the case of magnetic tapes, such devices generally function best when the leading edge of the tape is provided with a leader block. One widely used leader block is described in U.S. Pat. No. 4,383,660 ("the -660 patent") and the teachings of this patent are hereby incorporated into this patent disclosure. The rear portions of such leader blocks are provided with tape gripping means such as pin and groove arrangements which serve to connect the leading edge of the tape to the leader block. The forward portions of these leader blocks are usually provided with a cylindrical slot for receiving a mating cylindrical threader pin suspended from the underside of a threader arm. Typically the cylindrical threader pin consists of a shaft which terminates in an enlarged member which engages with a similarly enlarged opening in the leader block. Typically these enlarged members are given a cylinder configuration. Consequently, an enlarged member having a cylinder configuration will engage with a like-contoured cylindrical slot in a leader block. Generally, the threader pin's enlarged member and the leader block's slot are designed to engage when the leader block's slot is moved downward to encompass the threader pin's enlarged base, for example in the manner shown in FIG. 5B of the -660 patent. The leader block's slot can be moved directly downward, i.e., parallel to the threader pin, or with a rotating downward motion such as that disclosed in U.S. patent application Ser. No. 872,951 whose teachings are hereby incorporated into this patent disclosure.
Most prior art magnetic tape threading devices employ rather complex pantoarm mechanisms to thread leader blocks from tape supply reels to take-up reels. One representative and widely used pantoarm assembly is disclosed in U.S. Pat. No. 4,399,936 ("the -936 patent"). Its most prominent feature is a powered, rotatable, pantoarm assembly which is mounted over a cam substrate. The cam substrate has an irregular, but generally elliptical-shaped cam groove. This cam groove, in cooperation with the pantoarm assembly, serves to define a complex, circumvoluted path over which the tape leader travels from the tape deck's supply reel to its take-up reel.
Its mechanism is rather complex. The first pantoarm element is a shaft linkage arm fixedly connected to a motor. A follower linkage is pivotally connected to its other end. The opposite end of the follower linkage cooperates with a tape leader of the type disclosed in the -660 patent. This follower linkage is also pivotally connected to a cam linkage. The opposite end of the cam linkage, in turn, is pivotally connected to a bearing which follows the contour of the cam groove. The shaft linkage and cam linkage are also interconnected by means of a linkage arm having pivot connections on each of its ends. In all, this particular pantoarm assembly has four linkage arms and five pivot connections.
Its operative motions are also rather complex. When the shaft linkage is rotated, the follower bearing, and hence the follower bearing end of the cam linkage, is pulled through the generally elliptical path defined by the cam groove. This follower bearing path, in turn, serves to determine the extension of the follower linkage which engages the tape leader. The full and exact details of this particular pantoarm assembly, as well as the circumvoluted path that it defines for the tape leader are best understood by referring to their detailed drawings; see for example FIGS. 2 and 3 of the -936 patent.
In any event, the forces associated with, and the complexities of, the motions which pantoarms of this type must undergo are such that their mechanisms tend to wear rather quickly. Such wear manifests itself in several ways. Vertical "play" develops. This is chiefly the result of horizontal wear at the pivot points of such pantoarm devices. Horizontal play also develops. This, however, is often more the result of cam groove wear. In all cases however, tape leader alignment and guidance, along the entire path from the supply reel to the take-up reel, soon deteriorates. Ultimately, wear upon such linkages, pivot mechanisms and cam grooves leads to malfunctions. In order to minimize and compensate for such wear, many pantoarm devices employ guides at various places along the path traveled by the leader block. Wear upon these pantoarm components also tends to produce dust and grit which often proves harmful to the entire tape deck system. Data reliability integrity is particularly sensitive to the harmful effects of dust and grit.